RT Journal Article SR Electronic T1 Endoplasmic reticulum membranes are continuously required to maintain mitotic spindle size and forces JF Life Science Alliance JO Life Sci. Alliance FD Life Science Alliance LLC SP e202201540 DO 10.26508/lsa.202201540 VO 6 IS 1 A1 Margarida Araújo A1 Alexandra Tavares A1 Diana V Vieira A1 Ivo A Telley A1 Raquel A Oliveira YR 2023 UL https://www.life-science-alliance.org/content/6/1/e202201540.abstract AB Membrane organelle function, localization, and proper partitioning upon cell division depend on interactions with the cytoskeleton. Whether membrane organelles also impact the function of cytoskeletal elements remains less clear. Here, we show that acute disruption of the ER around spindle poles affects mitotic spindle size and function in Drosophila syncytial embryos. Acute ER disruption was achieved through the inhibition of ER membrane fusion by the dominant-negative cytoplasmic domain of atlastin. We reveal that when centrosome-proximal ER membranes are disrupted, specifically at metaphase, mitotic spindles become smaller, despite no significant changes in microtubule dynamics. These smaller spindles are still able to mediate sister chromatid separation, yet with decreased velocity. Furthermore, by inducing mitotic exit, we found that nuclear separation and distribution are affected by ER disruption. Our results suggest that ER integrity around spindle poles is crucial for the maintenance of mitotic spindle shape and pulling forces. In addition, ER integrity also ensures nuclear spacing during syncytial divisions.